Integrated circuits are typically fabricated in monocrystalline silicon substrate. This substrate is expensive, leading to continual efforts to fabricate more circuitry within a given area of substrate. increasing density.
For nonvolatile memory, a highly effective approach to increase density is to build monolithic three dimensional memories above the substrate, like those disclosed in Johnson et al., U.S. Pat. No. 6,034,882: Johnson et al., U.S. Pat. Application No. 09/928,536, filed Aug. 13, 2001; Knall et al., U.S. Pat. No. 6,420,215; and Vyvoda et al., U.S. Pat. Application No. 10/185,507, filed Jun. 27, 2002, all hereby incorporated by reference in their ehtirety.
Such memories can be improved to achieve higher densities.